PROJECT SUMMARY The bone marrow (BM) microenvironment is a favorable microenvironment for tumor growth and a frequent destination for (i) metastasis, which contributes to over 90% of cancer-related deaths, and (ii) hematologic cancers such as multiple myeloma (MM), which remains incurable. Effective treatments for cancers that reside in BM remain elusive, in part, due to chemoresistance and a lack of safe and effective drug delivery systems. While efforts have largely focused on identifying and studying molecular mechanisms intrinsic to tumor cells that contribute to chemoresistance, new insights suggest that the BM microenvironment, and its physical interactions with tumor cells, enable disease progression and chemoresistance. Therefore, this underappreciated area of BM tumor biology merits consideration as a target for therapeutic intervention. However, the potential of these therapies is limited by (i) inefficient drug delivery to target cells in BM, and (ii) an incomplete understanding of how delivery system physicochemical properties and physiological factors affect BM delivery. In part, this is due to a large disconnect between how these systems are evaluated in an in vitro setting versus in vivo. Despite advances in in vitro platforms for drug screening, they remain a poor predictor of in vivo efficacy, where anatomical structures, biologics, and physiological forces interact with delivery systems and influence their final destination. Rather than selecting based on in vitro performance, there is an urgent need to innovate platforms that enable high-throughput screening in vivo. One approach to overcoming these challenges is to leverage innovative molecular barcoding technologies with next-generation deep sequencing techniques and bioinformatics, as means to accelerate therapeutic discovery. This proposal aims to develop a data-driven drug delivery (4D) platform that leverages interdisciplinary and quantitative approaches drawn from biomaterials science, nanotechnology, genomics, bioinformatics, and medicine to (i) develop an innovative technology platform where thousands of unique nanoparticle (NP) nucleic acid (siRNA, miRNA, mRNA, CRISPR-Cas9) delivery systems can be simultaneously evaluated in vivo, (ii) quantify delivery using deep sequencing and bioinformatics analysis of large datasets to develop structure-function criteria for delivering therapeutics safely and effectively into BM, and (iii) exploit NPs developed from 4D to therapeutically target BM, as a means to prevent tumor progression and chemoresistance. Of particular interest is to examine whether 4D can develop translational NP nucleic acid therapeutics for MM as a representative disorder, particularly for chemoresistant patients with survival rates of 3-6 months. Successful outcomes of this research will address critical technical barriers to progress in drug and gene delivery, hematologic cancers, metastasis, and many other related areas. Ultimately, we envision 4D will provide fundamentally new insights into in vivo physiological barriers and biological questions of interest to a broad range of Institutes at the NIH, which may contribute to the identification of new therapeutic targets and translational strategies.